Charging response of back-end-of-the-line barrier dielectrics to VUV radiation

The response of SiN, N-SiC, O-SiC, and SiC dielectrics of varying thickness deposited on Si substrates to irradiation with vacuum ultraviolet (VUV) was compared. The resulting charge was evaluated by measuring the surface potential on the dielectrics after irradiation with 9.5 eV photons. The surface potential on all of the dielectrics was positive due to charge accumulation in traps located within the dielectrics. By comparing the surface potential on several thicknesses of dielectrics after VUV irradiation we can determine whether the trapped charges are in the bulk of the dielectric or at the dielectric-substrate interface.     

Electrically Controlled Localized Charge Trapping at Amorphous Fluoropolymer–Electrolyte Interfaces

Charge trapping is a long‐standing problem in electrowetting on dielectric, causing reliability reduction and restricting its practical applications. Although this phenomenon is investigated macroscopically, the microscopic investigations are still lacking. In this work, the trapped charges are proven to be localized at the three‐phase contact line (TPCL) region by using three detecting methods—local contact angle measurements, electrowetting (EW) probe, and Kelvin probe force microscopy. Moreover, it is demonstrated that this EW‐assisted charge injection (EWCI) process can be utilized as a simple and low‐cost method to deposit charges on fluoropolymer surfaces. Charge densities near the TPCL up to 0.46 mC m^?2 and line widths of the deposited charge ranging from 20 to 300 µm are achieved by the proposed EWCI method. Particularly, negative charge densities do not degrade even after a “harsh” testing with a water droplet on top of the sample surfaces for 12 h, as well as after being treated by water vapor for 3 h. These findings provide an approach for applications which desire stable and controllable surface charges.     

Dielectric properties of electron irradiated PbZrO<Subscript>3</Subscript> thin films

The present paper deals with the study of the effects of electron (8 MeV) irradiation on the dielectric and ferroelectric properties of PbZrO₃ thin films grown by sol-gel technique. The films were (0.62 μm thick) subjected to electron irradiation using Microtron accelerator (delivered dose 80, 100, 120 kGy). The films were well crystallized prior to and after electron irradiation. However, local amorphization was observed after irradiation. There is an appreciable change in the dielectric constant after irradiation with different delivered doses. The dielectric loss showed significant frequency dispersion for both unirradiated and electron irradiated films. T _c was found to shift towards higher temperature with increasing delivered dose. The effect of radiation induced increase of ɛ′(T) is related to an internal bias field, which is caused by radiation induced charges trapped at grain boundaries. The double butterfly loop is retained even after electron irradiation to the different delivered doses. The broader hysteresis loop seems to be related to radiation induced charges causing an enhanced space charge polarization. Radiation-induced oxygen vacancies do not change the general shape of the AFE hysteresis loop but they increase P _s of the hysteresis at the electric field forced AFE to FE phase transition. We attribute the changes in the dielectric properties to the structural defects such as oxygen vacancies and radiation induced charges. The shift in T _C, increase in dielectric constant, broader hysteresis loop, and increase in P _r can be related to radiation induced charges causing space charge polarization. Double butterfly and hysteresis loops were retained indicative of AFE nature of the films.     

Temperature-dependent memory characteristics of silicon-oxide-nitride-oxide-silicon thin-film-transistors

This study investigates the temperature-dependent memory characteristics of polycrystalline silicon thin-film transistors with oxide/nitride/oxide stack gate dielectrics and N⁺ poly-Si gate structures for nonvolatile memory application. As the device was programmed by Fowler-Nordheim tunneling at high temperature, some electrons captured in shallow traps could obtain enough thermal energy to de-trap to the gate, resulting in low programming efficiency. As the programming time increases, the hole injection through the blocking oxide from the gate would further lead the threshold voltage to decrease. In addition, the retention characteristic of the device programmed at higher temperature exhibits better charge storage ability. Because the electrons trapped in the shallow traps of the nitride layer can be easily de-trapped when temperature rises, the memory characteristics are mainly dominated by charges stored in the deep traps.     

Ag and O ion irradiation induced improvement in dielectric properties of the Ba(Co1/3Nb2/3)O3 thin films

We present the preliminary results of temperature and frequency dependent dielectric measurements on Ba(Co_1/3Nb_2/3)O₃ (BCN) thin films. These films were prepared on indium tin oxide (ITO) coated glass substrates by the pulse laser deposition (PLD) technique. It exhibits single-phase hexagonal symmetry. These films were irradiated with Ag¹⁵⁺ (200 MeV) and O⁷⁺ (100 MeV) beams at the fluence 1 × 10¹¹, 1 × 10¹², and 1 × 10¹³ ions/cm². On irradiating these films, its dielectric constant (?′) and dielectric loss (tan δ) parameters improve compared to un-irradiated film. Compared to O⁷⁺ irradiation induced point/cluster defects Ag¹⁵⁺ induced columnar defects are more effective in reducing/pinning trapped charges within grains. The present paper highlights the role of swift heavy ion irradiation in engineering the dielectric properties of conductive samples to enable them to be useful for microwave device applications.     

Investigation of alumina-silica films deposited by pulsed injection metal-organic chemical vapour deposition

This work is devoted to deposition of alumina-silica films using an innovative pulsed injection metal organic chemical vapour deposition technique and aluminium tri(iso-propoxide) (Al(i-OPr)₃) and tetraethoxysilane (TEOS) as precursors. The deposited aluminium silicate films have been characterised by scanning electron microscopy, infrared spectroscopy, X-ray diffractometry and capacitance-voltage (C-V) measurements. The investigation of the deposition at different Si/Al ratios and substrate temperatures has shown that the growth rate increases with the increase of Al(i-OPr)₃ proportion in solution and decreases as the proportion of TEOS increases. We have also shown that aluminium content in the film increases at lower deposition temperatures while silicon content increases at higher temperatures. The permittivity of the films determined from C-V measurements decreases with increasing substrate temperature. It was found that films deposited at substrate temperatures of 600 or 700 °C and with the highest Si/Al ratio have the lowest dielectric permittivity. This research should be useful for further development of MOCVD technology for the deposition of aluminosilicate-based dielectric materials with controlled dielectric permittivity.     

Porogen residues detection in optical properties of low-k dielectrics cured by ultraviolet radiation

The optical properties of low dielectric constant (low-k) films have been determined by variable angle spectroscopic ellipsometry in the range from 2 eV to 9 eV to characterize the process of porogen removal during the UV-cure. The studied carbon doped oxide (SiCOH) porous dielectric films have been prepared by plasma enhanced chemical vapor deposition. The films have been deposited as a composition of a matrix precursor and an organic porogen. After deposition, the films have been cured by thermal annealing and UV irradiation (λ = 172 nm) to remove the porogen and create a porosity of 33%, reaching a dielectric constant of 2.3. The process of porogen decomposition and removal has been studied on series of low-k samples, UV-cured for various times. Additional samples have been prepared by the deposition and curing of the porogen film, without SiCOH matrix, and the matrix material itself, without porogen. The analysis of the optical response of the porous dielectric as a mixture of matrix material, porogen and voids, together with Fourier transform infrared analysis, allows the sensitive detection of the volume of the porogen and indicates the existence of decomposed porogen residues inside the pores, even for long curing time. The variation of the deposition and curing conditions can control the amount of the porogen residues and the final porosity.     

Contrast inversion in electrostatic force microscopy imaging of trapped charges: tip-sample distance and dielectric constant dependence

We present a numerical and analytical study of the behavior of both electrostatic force and force gradient created by a charge trapped below the surface of a dielectric on an atomic force microscope tip as a function of the dielectric constant and tip-sample distance. As expected, the force decreases monotonously when the dielectric constant increases. However, a maximum in the dielectric constant dependence of the force gradient is found. This maximum occurs in the typical experimental parameters' range and depends on the tip-sample distance and the sample thickness. The analytical study permits us to understand the physical origin of this phenomenon and is in good agreement with the numerical simulation for small tip-sample distances. We also report a study exemplifying a possible contrast inversion in electrostatic force microscopy (EFM) signals while scanning, at different heights, two charges trapped in a sample having heterogeneous dielectric domains. In addition to this particular contrast inversion effect, this study can be considered as a way to gain insight into the mechanisms of EFM image formation as a function of the dielectric constant and tip-sample.     

Microstructure and chemical analysis of Hf-based high-k dielectric layers in metal-insulator-metal capacitors

The microstructure and chemistry of the high-k gate dielectric significantly influences the performance of metal-insulator-metal (MIM) and metal-oxide-semiconductor devices. In particular, the local structure, chemistry, and inter-layer mixing are important phenomena to be understood. In the present study, high resolution and analytical transmission electron microscopy are combined to study the local structure, morphology, and chemistry in MIM capacitors containing a Hf-based high-k dielectric. The gate dielectric, bottom and gate electrodes were deposited on p-type Si(100) wafers by electron beam evaporation. Four chemically distinguishable sub-layers were identified within the dielectric stack. One is an unintentionally formed 4.0 nm thick interfacial layer of Ta₂O₅ at the interface between the Ta electrode and the dielectric. The other three layers are based on HfN_xO_y and HfTiO_y, and intermixing between the nearby sub-layers including deposited SiO₂. Hf-rich clusters were found in the HfN_xO_y layer adjacent to the Ta₂O₅ layer.     

Computer model of the trapping media in micro FLASH? memory cells

A computer model for the dielectric trapping layer in the microFLASH memory transistor is developed. Due to local trapping of injected charges in corresponding devices the problem of lateral charge migration in the plane parallel to the transistor channel becomes of principal importance. Molecular Dynamics method was used to design a cluster of atoms with dielectric properties and to perform computer simulation of the redistribution of the injected charges in the program/erase processes. The charge distributions obtained on the basis of proposed model are strongly influenced by Coulomb repulsion between the trapped charge carriers. This effect leads to non-Gaussian discrete space distribution of trapped charges and significantly influences the endurance of the memory device. We demonstrate that large densities of traps and injected carriers are strongly correlated, limiting the amount of charge that can be accumulated in the programming process. The model allows select optimum parameters of the trapping layer to ensure high retention properties of the memory cells.     

Computer model of the trapping media in micro FLASH® memory cells

A computer model for the dielectric trapping layer in the microFLASH memory transistor is developed. Due to local trapping of injected charges in corresponding devices the problem of lateral charge migration in the plane parallel to the transistor channel becomes of principal importance. Molecular Dynamics method was used to design a cluster of atoms with dielectric properties and to perform computer simulation of the redistribution of the injected charges in the program/erase processes. The charge distributions obtained on the basis of proposed model are strongly influenced by Coulomb repulsion between the trapped charge carriers. This effect leads to non-Gaussian discrete space distribution of trapped charges and significantly influences the endurance of the memory device. We demonstrate that large densities of traps and injected carriers are strongly correlated, limiting the amount of charge that can be accumulated in the programming process. The model allows select optimum parameters of the trapping layer to ensure high retention properties of the memory cells.     

Total dose radiation effects of Au/PbZr0.52Ti0.48O3/YBa2Cu3O7-δ capacitors

PbZr_0.52Ti_0.48O₃/YBa₂Cu₃O₇₋δ (PZT/YBCO) thin films have been fabricated on Y₂O₃ stabilized zirconate (YSZ) substrates by a pulsed excimer laser deposition (PLD) method. In order to investigate total dose radiation effects on the Au/PZT/YBCO ferroelectric capacitor, the capacitance–voltage (C–V) curves and the retained polarization property of the capacitor have been measured before and after γ-ray irradiation. The results showed that, with an increased total dose, the retained polarization and the dielectric constant decreased, but the coercive field drifted towards positive voltage direction. This is caused by charges trapped by defects in the PZT capacitor during irradiation.     

Study on electrical degradation of p-type low-temperature polycrystalline silicon thin film transistors with C-V measurement analysis

Laser recrystallized low-temperature poly-silicon (LTPS) films have attracted attention for their application in thin-film transistors (TFTs), which are widely used in active matrix display. However, the degradation behavior of p-type LTPS TFTs is not quite clarified yet. In this paper, the instability mechanisms of p-channel LTPS TFTs under DC bias stress have been investigated. From the IV transfer curves, it was observed that LTPS TFT's mobility increases after stress at some bias conditions. This degradation is most likely caused by interface traps between the poly-Si thin film and the gate insulator, as well as the damaged junction of the drain from stress. In this work, the assumption is examined via C-V measurement. It is found that the C_GD curves of the stressed TFT slightly increase for the gate voltage smaller than the flat band voltage V_FB. However, the C_GS curves of the stressed device are almost the same as those before stress. By employing simulation, it is found that the degradation of p-type TFTs under this stress condition is mainly caused by the trapped charges at the interface between the gate and the drain region, which is generated by the high voltage difference applied during DC bias stress.     

rf-Magnetron sputter deposited ZrO2 dielectrics for metal-insulator-semiconductor capacitors

ZrO₂ gate dielectric thin films were deposited by radio frequency (rf)-magnetron sputtering, and its structure, surface morphology and electrical properties were studied. As the oxygen flow rate increases, the surface becomes smoother. The experimental results indicate that a high temperature annealing is desirable since it improves the electrical properties of the ZrO₂ gate dielectric thin films by decreasing the number of interfacial traps at the ZrO₂/Si interface. The carrier transport mechanism is dominated by the thermionic emission.     

Electrical properties of diamond-like carbon films grown using ECR plasma decomposition of methane

Diamond-like carbon films were deposited on p-type silicon substrates by ECR-plasma decomposition of methane. The films have been characterized by scanning electron microscopy and Fourier transformed infrared spectroscopy. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured allowing interface trapped charges to be estimated. The density of states near to the Fermi level was calculated from the measurements to be of the order of 10¹⁹ cm⁻³ eV⁻¹.     

Electron Transfer in Nanoscale Contact Electrification: Photon Excitation Effect

Contact electrification (CE) (or triboelectrification) is a well‐known phenomenon, and the identity of the charge carriers and their transfer mechanism have been discussed for decades. Recently, the species of transferred charges in the CE between a metal and a ceramic was revealed as electron transfer and its subsequent release is dominated by the thermionic emission process. Here, the release of CE‐induced electrostatic charges on a dielectric surface under photon excitation is studied by varying the light intensity and wavelength, but under no significant raise in temperature. The results suggest that there exists a threshold photon energy for releasing the triboelectric charges from the surface, which is 4.1 eV (light wavelength at 300 nm) for SiO₂ and 3.4 eV (light wavelength at 360 nm) for PVC; photons with energy smaller than this cannot effectively excite the surface electrostatic charges. This process is attributed to the photoelectron emission of the charges trapped in the surface states of the dielectric material. Further, a photoelectron emission model is proposed to describe light‐induced charge decay on a dielectric surface. The findings provide an additional strong evidence about the electron transfer process in the CE between metals and dielectrics as well as polymers.     

The structures of low dielectric constant SiOC thin films prepared by direct and remote plasma enhanced chemical vapor deposition

Two structures of low dielectric constant (low-k) SiOC films were elucidated in this work. Low-k thin film by remote plasma mode was mainly composed of inorganic Si-O-Si backbone bonds and some oxygen atoms are partially substituted by CH₃, which lowers k value. The host matrix of low-k thin films deposited by direct plasma mode, however, was mainly composed of organic C-C bonds and “M” and “D” moieties of organosilicate building blocks, and thus the low dipole and ionic polarizabilities were the important factors on lowering k value.     

耐电晕聚酰亚胺薄膜表面电荷特性

为了解微纳米尺度下聚合物绝缘材料表面电荷生成、发展规律和机理,利用电场力显微镜（electrostatic force microscope,EFM）研究了两种聚酰亚胺薄膜的表面电荷生成及其衰减特性.采用EFM的导电探针在聚酰亚胺薄膜表面注入电荷,并对产生的电荷进行原位表征,结果表明原始（100 HN）和耐电晕（100 CR）两种聚酰亚胺薄膜上电荷生成和衰减特性不同.耐电晕薄膜被注入的表面电荷数量少且注入后衰减较快,其衰减服从指数规律,衰减时间常数为19.9 min;原始薄膜被注入的电荷量较多,衰减时间常数为48.1 min.分析表明,耐电晕薄膜中由于掺杂了Al2O3成分,使得材料的介电常数提高、电阻率下降.介电常数提高使得金属-电介质界面势垒提高,增加了电荷注入难度,导致表面电荷数量少;电阻率下降使得电荷消散速度加快.     

Observation and cancellation of a perturbing dc stark shift in strontium optical lattice clocks

We report on the observation of a dc Stark frequency shift at the 10-(13) level by comparing two strontium optical lattice clocks. This frequency shift arises from the presence of electric charges trapped on dielectric surfaces placed under vacuum close to the atomic sample. We show that these charges can be eliminated by shining UV light on the dielectric surfaces, and characterize the residual dc Stark frequency shift on the clock transition at the 10-(18) level by applying an external electric field. This study shows that the dc Stark shift can play an important role in the accuracy budget of lattice clocks, and should be duly taken into account.     

Study of reactive sputtering titanium oxide for metal-oxide-semiconductor capacitors

Metal oxide semiconductor (MOS) capacitors with titanium oxide (TiO_x) dielectric layer, deposited with different oxygen partial pressure (30, 35 and 40%) and annealed at 550, 750 and 1000 °C, were fabricated and characterized.Capacitance-voltage and current-voltage measurements were utilized to obtain, the effective dielectric constant, effective oxide thickness, leakage current density and interface quality. The obtained TiO_x films present a dielectric constant varying from 40 to 170 and a leakage current density, for a gate voltage of − 1 V, as low as 1 nA/cm² for some of the structures, acceptable for MOS fabrication, indicating that this material is a viable high dielectric constant substitute for current ultra thin dielectric layers.